One design criterion for a circuit breaker holds that upon occurrence of a load fault which creates an unacceptably large current draw (e.g., a short circuit current) through closed contacts of a circuit breaker, the circuit breaker mechanism must open the contacts in a manner that promptly terminates the current. Certain known circuit breakers that employ one or more pivotally mounted contact arms utilize electromagnetic blow-apart, or blow-open, force to blow open the contact arm(s) upon the occurrence of such a sudden load fault. Although the blow-open force quickly initiates contact arm motion to begin tripping the circuit breaker, current may continue to arc across the contacts as the contact arm(s) swing open. Consequently, further circuit breaker design principles include minimizing (and ideally eliminating) such arcing as the tripping continues. Furthermore, once current flow has terminated, any opportunity for its re-establishment must be foreclosed as the tripping concludes.
In accomplishing prompt arrest of current arcing across blowing-open contacts, it may be desirable for the circuit breaker mechanism to augment the impetus of the blow-open force as the tripping continues toward conclusion. But in doing so, the mechanism's augmentation of the force acting on the swinging contact arm(s) must not induce rebound of the contact arm(s) off of a stop to an extent that could potentially re-establish current flow.
Consider for example a circuit breaker that employs a spring-loaded, over-center toggle mechanism which goes over-center during the trip. As the mechanism goes over-center, an operating spring which had been effectively applying to the contact arm(s), a force resisting, but not preventing, the trip, now suddenly applies its force to aid the trip, driving the swinging contact arm(s) against the stop. That added force must not cause excessive contact arm rebound from the stop.
Circuit breaker design must therefore take into consideration various factors that may conflict. A better circuit breaker design will account for such factors to provide a circuit breaker that will terminate a specified fault current within a specified response time, with better assurance that current will not be re-established once the circuit breaker has been tripped. Moreover, a successful circuit breaker design should be cost and space efficient.
It is toward these and other objectives that the present invention is directed.
A circuit breaker comprises a cross bar and one or more contact arms that are joined together by a cylindrical hinge pin to form an assembly that is mounted within the circuit breaker housing. This hinge pin allows pivotal movement of the assembly about the hinge axis, accompanied by allowance of limited relative movement between each such contact arm and the cross bar. When a fault occurs, a blow-open force acting on the contact arm allows the contact arm to begin swinging slightly before the cross bar begins to move. This feature is intended to promote faster response to a fault since the inertia of the cross bar does not have to be overcome to initiate contact separation.
The cross bar contains spaced apart walls that provide a space for receiving a corresponding contact arm between them. These walls contain bent slots, generally transverse to the length of the corresponding contact arm, and the corresponding contact arm contains a generally straight slot running generally lengthwise of the contact arm and generally transverse to the swinging motion of the contact arm. A cylindrical blow-open pin passes through the walls' slots and the contact arm slot such that motion of the contact arm relative to the cross bar causes the blow-open pin to travel within the respective slots. If there are plural contact arms similarly pivotally mounted on a common cross bar, each one also has a generally straight slot, and the immediately adjacent side walls of the cross bar contain bent slots. A separate blow-open pin passes through each contact arm slot and the bent slots in the immediately adjacent side walls of the cross bar.
In other arrangements the blow-open pin has been spring-loaded by one or more small springs that are disposed between the cross bar and a blow-open pin to bias the blow-open pin away from the hinge axis of the cross bar/contact arm assembly. Once a blow-open pin has traveled in one direction from a first segment of the bent slots, past the knees of the bent slots, and into a second segment of the bents slots during blowing-open, such springs urge the blow-open pin to stay in the second segment of the bent slots. During initial contact arm rebound from a stop, a blow-open pin travels in the opposite direction back across the knees of the bent slots whereupon the springs urge the blow-open pin to stay in the first segments of the bent slots. Such springs have previously been disposed outboard of the side walls of the cross bar that contain the bent slots.
The present invention relates to a construction that provides a more efficient use of space for locating a spring that biases a blow-open pin. Each contact arm comprises a straight elongate through-slot that runs generally lengthwise of the contact arm and is closed at both lengthwise ends. Adjacent each slot, each respective side wall of the cross bar contains a bent slot having a knee. A respective cylindrical blow-open pin passes through all three of these slots. A small helical coiled spring occupies each contact arm slot and is compressed between the blow-open pin and the end of the contact arm slot that is proximate the cross bar/contact arm hinge axis. Each such spring is laterally confined by the adjacent side walls of the cross bar so as to remain in this position in the respective contact arm slot. Thus, each such spring acts between the blow-open pin and the respective contact arm to bias the blow-open pin in a direction away from the cross bar/contact arm hinge axis. It is believed that this construction eliminates the need for space between adjacent pairs of cross bar side walls to accommodate the springs that bias the blow-open pin.
Accordingly, one aspect of the present invention relates to a circuit breaker comprising a contact arm having a pivot axis, a mounting pivotally mounting the contact arm about its pivot axis for swinging motion to break a circuit, spaced apart side walls which are proximate lateral sides of the contact arm and with respect to which the contact arm can swing, a through-opening in the contact arm that defines a slot whose length is generally transverse to the swinging motion of the contact arm, a pin that passes through the contact arm's slot but is constrained by the slot for travel along the slot's length, the spaced apart side walls comprising slots which receive portions of the pin and which constrain the pin to travel lengthwise of the side walls' slots, a spring disposed in the contact arm slot and confined laterally by the spaced apart side walls to exert a force on the pin urging the pin along the length of the contact arm slot, and wherein relative motion between the contact arm and the side walls causes the pin to travel lengthwise of the contact arm's slot and lengthwise of the side walls' slots, changing the spring force exerted by the spring on the pin.
Another aspect of the present invention relates to a circuit breaker comprising a contact arm having a pivot axis, a mounting pivotally mounting the contact arm about its pivot axis for swinging motion to break a circuit, the contact arm having a through-opening whose length is generally transverse to the swinging motion of the contact arm, a pin that passes through the contact arm's through-opening but is constrained by the through-opening for travel along the through-opening's length, a slotted track disposed beside the contact arm and engaging the pin to constrain the pin to travel lengthwise of the slotted track, a spring contained in the contact arm through-opening to exert a force on the pin urging the pin along the length of the contact arm slot, and wherein relative motion between the contact arm and the slotted track causes the pin to travel lengthwise of the contact arm's slot and lengthwise of the slotted track, changing the spring force exerted by the spring on the pin.
Yet another aspect of the present invention relates to an elongate contact arm having lengthwise opposite end portions between which is an intermediate portion, one lengthwise end portion comprising a pivot axis for mounting the contact arm for swinging motion about a pivot axis, the other lengthwise end comprising a contact, and the intermediate portion comprising an elongate through-slot having a length in the same direction as the length of the contact arm.
The foregoing, along with further features, advantages, and benefits of the invention, will be seen in the ensuing description and claims, which are accompanied by drawings. The description and drawings disclose a presently preferred embodiment of the invention according to the best mode contemplated at this time for carrying out the invention.